Thermoelectric generating assembly

ABSTRACT

A thermoelectric generating assembly in which heat is produced by mixing air and fuel and causing the mixture to pass over a combustion member, the degree of heat being controlled by varying the amount of air and means being provided to equalize the air pressures at the air inlet to and the exhaust from the combustion chamber. The combustion chamber provides heat to a thermoelectric module comprising thermoelectric generating elements sealed in an evacuated space between walls having flexible portions, those walls including relatively thick portions of good heatconductivity.

waited Sites stem Martin A. Rubinstein Morrisville, Pm;

Charles Telekl, West Orange, NJ. [21 Appl. No. 488,483

[22] Filed Sept. 20, 1965 [72] Inventors [45] Patented Dec. 14, 1971 [73] Assignee Isotopes, Incorporated Westwood, NJ.

[54] THERMOIELECTRIC GENERATING ASSEMBLY 6 Claims, 9 Drawing Figs.

[52] US. Cl. [36/205, 136/208, 136/217, 136/221, 136/223 [51] Int. Cl. H01vl/00, H0lv1/02,H01v 1/30 [50] Fleld 01 Search ..136/200-212.

[56] References Cited UNITED STATES PATENTS 472,261 4/1892 Gulcher 136/209 109,603 11/1870 Farmer 136/208 3,056,848 10/1962 Meyers 136/210 3,111,432 11/1963 Sickert etal. 136/203 3,197,343 Palmatier, 136 /212 3,266,944 8/1966 Spira et a1 136/202 3,269,873 8/1966 Dent.... 136/208 3,291,199 12/1966 Gutzeit 431/157 3,325,312 6/1967 Sonntag, Jr 136/212 3,347,711 10/1967 Banks, Jr. et al. 136/202 375,242 12/1887 Acheson 136/205 X 2,675,417 4/1954 Heibel.... 136/209 3,057,940 10/ l 962 Fritts 136/233 3,198,240 8/1965 Keith et a1. 431/329 3,202,204 8/1965 J0uard.... 431/329 3,234,048 2/1966 Nelson 136/210 X 3,237,679 3/1966 Best..... 431/329 3,351,498 11/1967 Shinn eta 136/205 Primary Examiner-Winston A. Douglas Assistant Examiner-M. .l. Andrews Attorney-James and Franklin ABSTRACT: A thermoelectric generating assembly in which heat is produced by mixing air and fuel and causing the mixture to pass over a combustion member, the degree of heat being controlled by varying the amount of air and means being provided to equalize the air pressures at the air inlet to and the exhaust from the combustion chamber. The combustion chamber provides heat to a thermoelectric module comprising thermoelectric generating elements sealed in an evacuated space between walls having flexible portions, those walls including relatively thick portions ofgood heat-conductivity.

PATENTED DEC 1 41s" SHEET 1 0F 6 PATENTEU 050141971 SHEET 5 [1F 6 THERMOIELECTRIC GENERATING ASSEMBLY The present invention relates to the construction of a thermoelectric generator, and in particular to such a construction in which the efficiency of the transfonnation of energy from fuel to electricity is enhanced and in which the reliability of the apparatus to produce such energy conversion over wide ranges of ambient conditions is greatly increased.

The use of thermoelectric electrical generators for providing electrical energy, particularly in remote locations where normal sources of electric power are not available or as emergency power sources for use when normal power sources fail, is growing. Two primary limitations on the use of such equipment are efficiency and reliability.

The more electrical energy that can be produced from a given amount of fuel, the less costly is that energy, and the longer can the equipment be operated without having to replenish the fuel supply. Thus improvement in overall efficiency is an obvious need with equipment of this type.

The problem of reliability arises to a large extent from the existence of very large temperature differentials and temperature variations in connection with the operation of the equipment. Parts must be in intimate connection with one another in order that heat may be transferred therebetween, and such intimate contact must in many instances be accomplished over comparatively large surface areas. Nevertheless, the parts in contact are formed of different materials which expand at different rates, and hence as temperatures change stresses are produced which, when intense enough or when fluctuated over a sufficiently long period of time, tend to cause physical failure of mechanical parts.

It is the prime object of the present invention to provide a thermoelectric generator assembly construction which solves the above-mentioned problems in a manner much more effective than any that have been know heretofore, and to do so by means of a construction which facilitates assembly and minimizes cost.

In the fonn here specifically disclosed the generator is designed to use a gaseous fuel such as propane which, when mixed with air in appropriate proportions, will bum without flame and will produce large quantities of heat. This buming" is accomplished by causing the fuel-air mixture to pass over the surface of a suitable combustion member, generally provided in the form of a screen through which the fuel-air mixture can pass. This member may be catalytic relative to the fuel-air mixture, in which case it may be maintained at a temperature below the normal ignition temperature of the fuel-air mixture, or it may be of the surface combustion type, in which case it is maintained at or above that normal ignition temperature. .In either case the combustion process takes place on the surface of the member at a temperature much lower than in a flame-type burner. Most of the heat energy liberated by the combustion is transferred from the member to the heat-receiving surfaces of the assembly by infrared radiation. Some of the heat energy liberated acts upon the products of combustion so as to raise their temperature, and a portion of this heat energy is transferred to the heat-receiving surfaces of the unit as the exhaust products pass over those surfaces. The remainder of the heat energy is lost with the combustion products as they exhaust from the unit.

In order to facilitate the transfer of heat energy from the combustion area adjacent the catalytic or surface combustion member to the heat-receiving surfaces of the unit, and provide for increased efficiency in the operative use of that energy, the combustion chamber is so designed as to maximize the active area of the combustion member and to ensure that said active area is in proper operative relationship with the functionally effective heat receiving surfaces. To that end the combustion chamber is here taught as being subdivided into a plurality of sections by means of wall elements which are spaced from one another and which are in substantially direct thermal communication with that wall of the combustion chamber through which heat is adapted to be applied to the hot sides of the generating elements themselves. These wall elements, here disclosed in the form of fins, are located closely adjacent to the combustion member and, indeed, define a structure about which the combustion member may be enfolded. As a result both the combustion member surface area and the heatreceiving surface area are maximized and are so spatially related as to facilitate efficient infrared heat transmission.

Moreover, the specific conditions of combustion are controlled in a novel and strikingly simple fashion, thereby to permit variation in the amount of heat which is efiectively utilized to produce electrical energy. This is done by controlling the amount of air which mixes with the fuel. For a given assembly there is an optimum air inlet rate for a given fuel flow rate, which will give rise to maximum heat production. If the air flow is permitted to occur at a greater or lesser rate than said optimum rate, less of the available heat will be utilized. A venturi device is used for aspirating the air into the fuel. By adjusting the size of the passage through which that airflows, either before it is aspirated into the fuel or after the air and fuel have bumed and are exhausting from the unit, the amount of effective air may be varied. When the passage size control is located in the exhaust passage from the combustion chamber the effect of external wind on the pressures within the unit is minimized, and consequently location of the restriction in the exhaust passage is preferred.

in order to take care of the problems presented by the wide ranges of temperature to which the operative parts are subjected and the differential expansion problems produced thereby, the thermoelectric generating module, the combustion chamber means engaged with its hot side, and the heat dissipating means engaged with its cold side, are all connected together in a fashion such as to permit effective and efficient heat transfer while permitting those parts movement relative to one another to compensate for differences in thermal expansivity. Moreover the thermoelectric generating module itself may incorporate the same principle of assembly.

In the module itself the thermoelectric elements are mounted within a casing comprising thin flexible walls which are sealed to one another radially beyond the thermoelectric elements, the interior of that casing being evacuated. The module also comprises relatively thick, rigid heat transmissive members the outwardly facing surfaces of which are preferably smooth and fiat. Atmospheric pressure, acting through the flexible casing walls upon the evacuated interior of the casing, forces the heat transmissive members axially into firm engagement with the hot and cold sides respectively of the generating elements, while permitting lateral movement of the walls relative to the thermoelectric elements when temperatures change and the engaged parts expand or contract to different degrees. Although the heat transmissive members are rigid, this action is not interfered with and said heat transmissive members are nevertheless in good heat-transfer relation with said generating elements via said thin walls. Thus only minimal stresses are exerted on the thermoelectric elements themselves as temperatures change. As a result the reliability of these elements, in general the most fragile parts of the entire assembly, is greatly increased. Because the same type of lateral sliding movement to relieve differentials in thermal expansion is provided for between the module on the one hand and the combustion chamber means and the heat-dissipating means respectively on the other hand, temperaturechange-induced stress at the interfaces between those elements are greatly minimized while effective heat transfer across those interfaces is accomplished. in addition, the design also prevents buildup of excessive compressive stresses on the thermoelectric elements, by making allowance for the fact that as the unit is brought up to operating temperatures the thicknesses of the module on the one hand and the dimension of the rigid members of the supporting structure on the other hand might vary relative to one another. The module is held in place by means of a spring relief mounting which permits variations in appropriate dimensions without any significant change in the spring forces.

When air is aspiration-mixed with fuel the amount of air which is thus aspirated will depend in part upon the pressures at the air inlet and exhaust portions of the system. Those pressures may tend to be differently affected by ambient conditions such as wind. A gust of wind which enters the unit will tend to increase the pressure inside the unit at the air inlet, thereby reducing the amount of air which mixes with the fuel and thus reducing the electric generating efficiency of the device. Means are provided for equalizing the pressure at the intake and exhaust portions of the fluid flow system, thereby to render the operation of the unit relatively insensitive to wind effects.

T o the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to the construction of a thermoelectric generating assembly, as defined in the appended claims and as described in this specification, taken together with the accompanying drawings, in which:

FIG. 1 is a three-quarter perspective view of a unit comprising two thennoelectric generating assemblies mounted in a typical application, to wit, positioned on a pole together with an associated piece of equipment for which it is to serve as a power supply;

FIG. 2 is a top plan view, partially broken away, of the generator unit of FIG. 11;

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is an end elevational view, partially broken away, of the unit of FIG. 1;

FIG. 5 is a cross-sectional view taken along the line 5-5 of FIG. 2;

FIGS. 6 and 7 are cross-sectional views taken respectively along the lines 66 and 7-7 of FIG. 5;

FIG. 8 is a top plan view, partially broken away, of an alternative embodiment of exhaust means for a plurality of generator assemblies; and

FIG. 9 is a cross-sectional view of an alternative embodiment of the thermoelectric module.

FIG. 1 illustrates a typical application for the thermoelectric generators of the present invention, those generators, generally designated A, being shown mounted on a pole B which also carries a work device C (for example, a microwave relay which is electrically connected to an antenna, not shown, also mounted on the pole B). The function of the generator assembly A is to provide electrical power for the work device C, either continuously or whenever a primary source of power should fail.

The generator A comprises a casing 2 which carries the operative parts, and which is provided with a base housing 4 adapted to be mounted on any suitable platform 6. The generator A is designed to be used in conjunction with a supply of fuel, which may take the form of one or more tanks of a suitable combustible gas such as propane, stored under pressure. The fuel supply tanks are not shown in the drawings. They are connected to the generator A by means of pipe 8 which enters the base housing 4 and is in fluid communication with pipe 10 in the casing 2. In the form here specifically disclosed, where two separate generating assemblies are incorporated into the same casing 2, the fuel pipe b may be connected to the individual fuel pipes 110 for each of the two assemblies via manifold 12.

(In the discussion to follow only single-generator assembly will be described, and it will be understood that the second generator is similarly constructed and arranged.)

The combustion chamber housing for the generator is generally designated 13. It comprises a flat end plate 141 to which a cover 16 is secured by means of nuts and bolts 17, a gasket 19 being interposed between the parts 14 and T6 at their periphery for sealing purposes. The plate M is generally flat, and defines that end wall of the combustion chamber housing through which heat is adapted to be transmitted to the thermoelectric generating elements. The cover 16 extends out from the plate M so as to define a space 18 therebetween. The

upper wall 20 of the cover 16 is provided, at a point remote from the plate Ml, with an opening 22 through which the venturi unit 24$ extends, that unit having a portion 26 extending above the wall 20 and a portion 2% extending into the space 118 and having a shaped fuel passage 30 formed therein. An orifice housing 32 is mounted on top of the venturi portion 26, and is there secured by means of screws 36. It has a depending conical portion 36 terminating in a passage 38. A tube 39 of appropriate inner diameter is fitted within the passage 38 and preferably extends up into the interior of the housing 32, where it may be surrounded by a conical mesh screen M. The housing portion 36 extends into the passage 40 in the venturi portion 26 and is radially inwardly spaced from the inner surfaces of the passage 40. An opening 42 is provided through the venturi portion 26 into the passage 40, and an air supply tube 414 is connected thereto, the other end of the air supply tube 44 being exposed to ambient air, as by opening into the base housing 4. The end 36 of the fuel feed line W is received inside the housing 32 at its upper end. The mouth 48 of the venturi unit 24 is spaced above the bottom wall 50 of the cover 116.

The use of the tube 39 permits highly accurate sizing of the orifice through which the fuel flows. The fact that the upper end of the tube 39 is above the bottom wall of the housing 32 minimizes the possibility that the tube 39 might become clogged by particles entrained in the fuel, and the screen 4ll provides additional protection in this regard.

Integrally formed with the wall 14, and extending therefrom into the space 18, are a plurality of wall elements 52, spaced laterally from one another and connected at their upper and lower ends by top and bottom walls 5 The edges 56 of the walls 54 which extend into the space 18 are recessed between the individual wall elements 52, as may best be seen in FIG. 7. A gas-permeable curtain 58 is secured to the edges 56, as by the screws 60 and strips 62 shown in FIG. 5, and extends between the top and bottom walls 54. The curtain 58 defines a combustion member, which may be of the surface combustion type but which is here specifically disclosed as being formed of a material which will catalyze the combustion of the fuel employed. The spaces between the wall elements 52 and the walls 54 define the primary combustion spaces or chambers 59.

For combustion-initiation purposes, resistance wire 64 is positioned on the venturi-side of curtain 58, preferably conforming in configuration, when viewed in plan, to the curtain 58, the wire 66 having its ends mounted on studs 66 which pass through the wall M and extend into the space 18. Electrical connections 68 are made to the studs 66 and hence to the resistance wire 64, those electrical connections extending through a suitable temperature sensitive switch (not shown) to a source of power (also not shown), which may be a storage battery designed to be maintained in charged condition by the operation of the thermoelectric generator itself.

The top wall 54 extends closely inside the upper wall 20 of the cover to, and a gasket 70 may be interposed therebetween for sealing purposes. The top wall 20 of the cover 116 carries an upwardly extending tubular portion 72. in which exhaust pipe 74 is received, the top cover wall 20 being cut away to define an opening 76 which provides access to the interior of the pipe 74, the gasket 70 being so shaped as not to obstruct the opening 76. The top wall 54 is provided with a plurality of apertures 78 which communicate between the primary combustion chambers 59, on the one hand, and the opening 76 and the exhaust pipe 741, on the other hand.

The exhaust pipe 74 extends through the top of the casing 2, where it is covered by a cap 80. The cap 80 is provided with an outer mounting portion $2 received inside aperture 84 formed in the top wall 86 of the casing 2 and there staked in place. The mounting portion 82 is surmounted by a radially inwardly extending wall 88 from which a tubular portion 90 depends, that tubular portion being snugly received inside the open upper end of the exhaust pipe 74$. A preferably separate part defined by a bottom wall 92 having an aperture 94 formed therein is received in the pipe 74 below the tubular portion 90,

the latter serving to retain part 92 in place. The diameter of the aperture 94 is smaller than the inner diameter of the pipe 74. A cover 96 is provided which may be secured to the wall 83 and extends radially therebeyond, where it is provided with depending sides 98, spaces 100 being provided between the cover 96 with its depending walls 98 and the remainder of the cap 80 through which exhaust gases can flow. The cover 96 prevents rain from entering the pipe '74 while permitting exhaust gases to vent therefrom.

The thermoelectric generating unit itself is provided in the form of the discrete module, generally designated 101, of which two specific embodiments are here disclosed. One embodiment is best shown in FIGS. 4 and 5 and the other is shown in FIG. 9. Insofar as the parts of the two embodiments are essentially the same, they will be designated by the same reference numerals, reference numerals for the embodiment of FIG. 9 being differentiated by being primed.

To described first the embodiment shown in FIGS. 4 and 5, the functionally operative portion thereof consists of an assembly 102 of thermoelectric generating elements appropriately arranged so as to have a hot side 104 and a cold side 106. The elements 102, here shown only in a generalized fashion because various forms of specific construction and arrangement are well known, are received within a casing formed of a hot side cover 108 and a cold side cover 110, both being formed of thin flexible material such as stainless steel sheet. The cold side cover 110 is essentially flat. The hot side cover 108 is provided with a peripheral flange 112 which is sealed to the peripheral portion of the cold side cover 110 in any appropriate fashion, and has a substantially flat central portion 114 connected to the peripheral flange 112 by bulged expansion portion 116. The hot and cold sides 104 and 106 of the thermoelectric generating elements 102 must be in good thermal connection with the casing covers 108 and 110, but must be electrically insulated therefrom. To that end there is interposed between the hot side 104 of the generating elements 102 and the hot side cover 108 a thin intervening twoply layer 118 which may consist of superposed shims of mica and lead, and there is interposed between the cold side 106 of the generating elements 102 and the cold side cover 110 a thin intervening two-ply layer 120 which may comprise a shim of mica with a layer of silicone grease loaded with thermally conductive particles such as aluminum powder superposed thereon. The mica and lead layer 118 and the mica and grease layer 120 play an important role. The mica plies of these layers provide for electrical insulation between the thermoelectric generating elements 102 and the module walls 108 and 110. The lead and grease portions of the layers 118 and 120 respectively provide mechanical compliancy permitting adaptation to the actual surface configuration of the inner surfaces of the module walls 108 and 110 and thus opposing surfaces of the thermoelectric elements 102. This is of particular importance because the inner walls of either surface of the module and the opposed surfaces of the elements 102 might well depart from an ideal flat and smooth characteristic. Particularly is this the case where the alternating N- and P-type thermoelectric elements comprising the element assembly 102 have different temperature coefficients of expansion. Moreover, between the opposed surfaces there should be no spaces which are not filled by a heat conductive material; otherwise the thermal contact between the hot and cold walls of the module and the generating elements 102 will be impaired. Both the lead layer and the aluminum-loaded silicon grease layer will conform under pressure to the exact shape of the inner module surfaces and the opposed thermoelectric element surfaces and will therefore ensure effective heat transmission.

The hot and cold side covers 108 and 110 extend out radially well beyond the generating elements 102 to the areas where they are sealed. The hot side cover 108 has secured to its outer surface in any appropriate manner, as by brazing, a comparatively thick rigid plate 122 fonned of a material such as tellurium copper or stainless steel, which has a very good heat transmission characteristic. The cold side cover has a comparable thick rigid plate 124 of heat-conductive material secured to its outer surface. Both of the plates 122 and 124 preferably extend laterally out beyond the thermoelectric generating elements 102, and their axially exposed surfaces preferably are made smooth and flat. The plates 122 and 124 may also be provided with central recesses 126 and 128 respectively extending inwardly from their axially exposed surfaces.

Electrical connection to the thermoelectric elements of the assembly 102 is made by means of terminals 130 which sealingly extend through the cold side cover 110 and are provided with external terminal portions 132 to which leads 134 may be connected. Also extending through the cold side cover 110, and exposed at the circumferential surface of the plate 124, is a tube 136 in fluid communication with the space between the covers 108 and 110. Once those covers have been sealed to one another with the generating elements 102 therewithin, the space between the covers is evacuated via the tube 136, after which the latter is sealed off.

it is not essential that the plates 122 and 124 be separated from the thermoelectric elements 102 by the walls 114 and 110. Thus, as shown in FIG. 9, the plates 122' and 124' may themselves constitute the upper and lower walls of the module casing, those plates being joined to another by flexible flanges 110' and 112', the latter being provided with bulged expansion portion 116'.

The heat dissipating unit, generally designated 137, comprises, as is relatively conventional, a wall 133 from which a plurality of spaced fins 140 extend outwardly. The wall 138 may be provided with an inwardly extending stud 142 which is adapted to be received within the aperture 128 in the plate 124 on the cold side of the module 101. The end plate 14 on the combustion chamber housing 13 may be provided with an enlarged integrally outwardly protruding portion 144, here shown as somewhat larger in diameter than the plate 122 on the hot side of the module 106, the portion 144 carrying a projecting stud 146 which is adapted to be received in the aperture 126 formed in the plate 122 on the hot side of the module 101. The studs 142 and 146 are preferably received somewhat loosely within the respective apertures 128 and 126.

Extending inwardly from the wall 138 of the heat dissipating unit 137 are a plurality of rods 148 which pass loosely through openings 140 formed in the secured together flanges of the plate 14 and cover 16 of the burner B and extend inwardly well beyond those flanges. The ends of the rods 148 are threaded at 152, and nuts 154 are received thereon, those nuts forcing washers 156 toward the aperture 150. Compression coil springs 155 are received on the rods 148 and are compressed between the washers 156 and the flanged portions of the cover 116 in which the apertures 150 are formed.

FIG. 8 discloses a modification of the exhaust system where a plurality of individual generating assemblies are provided. In that modification the exhaust pipes 74' from a plurality of such generators are each fitted over the inwardly extending ends of tubes 160 which pass through a wall 162 of the casing 2 and enter a manifold 164. The tube ends within the manifold 164 are laterally slotted at 166 and are internally threaded at 168, and externally threaded plugs 170 are received therein. The extent to which these plugs 170 are screwed into the tubes 160 will determine the effective size of those portions of the lateral slots 166 through which the exhaust gases can pass. The manifold 164 may be laterally surrounded by a casing 172 within which glass wool 174 or other suitable thermally insulating material is contained. The manifold 164 communicates in any appropriate manner with a stack 176 through which the exhaust gases can escape to the atmosphere.

An important feature of the design is the provision for minimizing effects of external air currents, such as winds, on the performance of the generator. The motive force imparted to the aspirated combustion air and to the exhausted products of combustion is provided solely by the momentum of the fuel emanating at high velocity from the tube 39, thereby to gions is different from that existing at the other region by thev same order of magnitude as the total pressure drop established by the venturi, then the flow of intake air will be significantly afiected, thus adversely affecting the performance of the burner. The direct pressure exerted by air currents or winds is 0.2, inches of water column at velocities of around 20 miles per hour and it increases as the square of the velocity tol.2 inchesv of water at 50 mph. and inches of water at 100 mph. Thus, it is seen that wind can have a very detrimental effect on the operation of the burner. This is minimized, in accordance with the present invention, by providing means to equalize the pressure at the intake and exhaust ends of theairflow system. Thus, as here specifically disclosed (see FIG. 3), the air intake tube 44 opens at its inlet end into an air pressure balancing chamber 45, defined by the basehousing 4. The space inside this chamber 45 communicates with the external ambient air by means of a number of relatively small holes 47 located on v the four sides and the bottom of the housing 45. The holes 37 on the sides are identical in number and size; the hole 47 on the bottom may comprise a total area which is larger than that on any of the sides. In addition, a relatively large tube 49 (ap proximately twice the diameter of the gas exhaust tube 741) vertically traverses the housing 2, one end of the tube 49 opening into the air balancing chamber-4S and the other end thereof penetrating the top cover 86 and provided with a .cover 80' similar to the cover 80 for the exhaust tube 74. The tube 49 thus establishes free fluid communication between the the balancing chamber 45 to the air intake tube 44. Thus, the pressures at the air intake and gas exhaust portions of the system are very close, if not the same, resulting in only minor changes in the combustion airflow which will not affect the burner performance appreciably.

It is desirable to fill the void spaces inside theenclosure by a good thermally insulating material, preferably fibrous mineral insulation. This reduces extraneous heat losses from the burner housing.

in operation the fuel such as propane gas, coming from a container where the fuel is maintained under pressure, flows through the pipes 8 and 10 into the housing 46 and through the venturi unit 24 into the space 18. The velocity of the fuel as it escapes from the tube 39 is quite high, since the fuel escapes from' that spud tip into an enlarged space it will aspirate air thereinto, the air entering via the opening 42 and the air supply tube 44. The air and the fuel mix in the lower portion of the venturi unit and in the space l8 to the left of the curtains 58 within the housing 13. This mixing is quite complete, largely because of the turbulence involved.

The fuel-air mixture then passesthrough the curtain 58 into the primary combustion chambers 59 which are laterally defined by a pair of adjacent wallelements 52, which are closed at their lower end by the lower wall 54, which are substantially closed at their upper end by the upper walls 54, and

. which are closed at their right-hand side, as viewed in FIG. 5,

air pressure balancing chamber 45 and the area at the top of Y the generator, thereby functioning as an air pressure balancing means. The way in which it works is as-follows:

a. If wind impinging on the exterior portions of the generaair forced into the balancing chamber 45 by'the wind through the openings 47 on these sides will tend to build up the pressure inside the chamber 45, and hence at the inlet of the air intake tube 44, relative to the pressure existing at the ends of the exhaust tubes 74. This will result in a tendency to increase the rate of combustion airflow into the generator. However, this pressure cannot build up appreciably since it will readily be relieved by air escaping from the balancing chamber through the holes 47 on the other two sides and the bottom and, mainly, through the large air balancing tube 49. The pressure increase is very low because, by design, the total area available for air leaving the balancing chamber is much larger than the total area where air is forced in by the wind.

b. If the wind velocity has a vertical, upward directed component, in addition to the horizontal components, the situation remains essentially the same as in case (a) except that now air also enters through the opening in the bottom; however, it must be realized that upward vertical components of the wind velocity cannot be large, since the generators are usually mounted relatively close to the ground and, additionally, any platform or other supporting structure will shield these openings from the wind.

c. If the wind velocity has a downward directed vertical component, a back pressure will be exerted upon the end of the exhaust tubes 74 which would nonnally tend to reduce the rate of combustion airflow into the generator. However, said back pressure is much lower than the direct velocity pressure exerted by the impinging wind due to the special configuration of cover 80. Moreover, that pressure is also exerted on the upper end of the balancing tube 49 and propagated through it down into by the wall 14. For starting't'he burning, when the catalytic curtain 58 is initially at low temperature, an electric current is passed through the heater wire 64, that wire raising the temperature of the catalytic curtain sufficiently high so thatcombustion of the gas will be initiated. Once combustion has occurred for a short period of time, the entire housing 13 is at a sufficiently high temperature so that the heater wire 64 is no longer needed to bring the curtain up to proper temperature for catalyzed combustion, and-when this situation has been attained the electric circuit to the heater wire 64 is interrupted, preferably by any conventional thermostatic switch.

Thecurtain 58 constitutes a combustion member which, depending upon its composition and the temperature to which it is raised, produces, initiates or controls combustion of the fuel-air mixture. A's here specifically disclosed the member 58 is in the form of a catalytic curtain, and under those circumstances it need be raised only to a temperature which is ap preciably below the normalignition temperature of the fuelair mixture. Should the composition of the member 58 be such as to produce noncatalytic surface combustion, the temperature of that member would have to be raised to a point equal to or higher than the normal ignition temperature of the fuelair mixture. In either case combustion occurs, and consequently heat is produced, at and over the surface of the member 58, and the bulk of the heat thus produced will be transmitted to the inner surfaces of the combustion chambers through radiation, primarily in the infrared range.

By virtue of the present construction, which provides a plurality of primary combustion chambers 59 each defined by projecting walls 52 around which the member 58 sinuously extends, the area of active surface of the member 58 at which combustion occurs is maximized, and that surface is so located relative to the heat-receiving walls of the combustion chamber that heat-transmission by radiation from the surfaces of the member 58 to those walls is effectively and efficiently accomplished. Thus, as may best be seen from FIG. 7, the extensive combustion-producing surfaces of the member 58 are located opposite and close to the inwardly facing surfaces of the walls 52.

The amount of combustion heat produced, and the proportion thereof which is effectively utilized, is determined in part by the rate at which fuel enters the system and in part by the amount of air which is mixed with a given amount of fuel. When the air-fuel mixture is in a predetermined optimum proportion the greatest amount of heat is effectively utilized. When the air-fuel ratio differs from that optimum value in either direction, the amount of heat utilized lessens. The air is drawn into mixture with the fuel by aspiration. The present construction provides that, for a given fuel flow, the amount of air mixed therewith can be brought to optimum value by providing a restriction of appropriate size in the flow path of the air. This restriction can be provided either in the air intake tube 44 or, as here specifically disclosed, in the exhaust pipe 74, that restriction being defined by the opening 94 in the wall 92. Placing the control orifice in the exhaust pipe 74 has the advantage that wind pressures active at the exhaust pipe cover 80 will not feed into the combustion chamber as readily when the restriction 94 is in place in the exhaust pipe as they would were that restriction not there located. For each installation a particular size for the aperture 94 is optimum. In the embodiment of P10. 8 the efi'ective size of the lateral slots 166 corresponds functionally to the different sizes of the aperture 94 in the embodiment of FIG. 4, and by screwing the plugs 170 into or out from the tubes 160 the effective sizes of those lateral slots 165 can be varied, thereby to achieve control of the proportion of airflow relative to fuel flow.

The manner in which the several units are secured to one another, and in which the individual elements of the thermoelectric generating module 101 are assembled, accomplishes three results: (1) Assembly of the parts is greatly facilitated; (2) Heat transfer is accomplished with a high degree of effectiveness; and (3) Stresses and strains attendant upon the temperature changes, with accompanying differences in thennal expansion of the individual components, are virtually eliminated.

To consider the thermoelectric module 101 first, the generating elements 102 are sandwiched between the plates 122 and 124. Because the module is sealed at its edges, because the space inside the module is evacuated, and because the peripheral walls are thin and flexible, atmospheric pressure presses the plates 122 and 124 (with or without interposed wall parts) firmly against the generating elements 102 and the layers 118, 120 interposed therebetween, thereby making good thennal transmissive contact and holding the generating elements 102 in position. The heavy plates 122 and 24 are rigid and flat, and will remain so during exposure to operating temperatures; this is essential for providing unifonn mechanical pressure forces and thermal contacts, and a uniform thermal flux to the individual thermoelectric elements. The peripheral flanges 110', 112 (or the corresponding parts in the embodiment of FIGS. 4 and 5) are preferably made of low thermal conductivity material to reduce heat shunt losses between the hot and cold sides of the module. They are also thin, thereby to provide flexibility to the enclosure to allow for expansion of the thermoelements when brought up to operating temperatures without appreciably changing the magnitude of the external pressures exerted upon them. They also provide for hermetic sealing of the module to enable evacuation of the inner cavity thereof. Such differences in thermal expansion as exist between the generating elements 102 and the plates 122 and 124 or the stainless steel walls 110 and 114 result merely in a sliding of the opposed surfaces of those elements relative to one another, without the development of any appreciable stresses or strains, since those surfaces are not positively secured to one another. The development of stresses due to dimensional changes in the axial direction of the thermoelectric elements and the module enclosure plates and rigid portions of the module support structure is substantially prevented by the flexible peripheral wall portions of the module on one hand, and the loading of springs 155 on the other hand, thereby permitting differential movement of the affected components relative to each other. Since the generating elements 102 are the most fragile parts of the assembly, and also the ones where cracks or breaks would most directly affect the operation of the entire unit, the virtual elimination of stresses in the generating elements 102 attendant on temperature change represents a significant increase in reliability and permits the units to be used under a wider range of temperature change than has formerly been the case.

While the pins 142 and 146 tend to center the module 101 and hold it in vertical position relative to the end plate 14 of the combustion chamber housing 13 and the wall 38 of the heat dissipating unit 137, although preferably with some degree of permitted play, it will be noted that the interfaces (a) between the hot side plate 122 of the module 101 and the portion 144 of the wall 14 of the combustion chamber housing 13, and (b) between the cold sideplate 124 of the module 101 and the wall 138 of the heat dissipating unit 134, are both free of positive connection, the parts being urged toward one another, with the module 101 held in sandwiched condition, by means of the springs 155. Hence here too differences in physical expansion arising from changes in temperature merely cause one of the surfaces at a given interface to slide over the other, while the surfaces remain pressed into close heattransmitting relationship. Thus throughout the unit, the problems involved in differential expansion attendant upon changes in temperature are greatly minimized, if not virtually eliminated.

Moreover, the mounting of the module 101 in nonpermanent fashion, solely by virtue of the springs 155, greatly facilitates replacement of individual modules 101 should that become necessary.

From the above it will be seen that a construction has been disclosed which is simple and comparatively inexpensive, which provides for thermoelectric generation in a more efficient manner than has previously been possible, which permits control and adjustment of the combustion temperature in a novel and effective fashion, which facilitates replacement and repair, and which minimizes the need for such replacement and repair by substantially eliminating the problems usually arising from the difl'erences in physical expansion attendant upon changes in temperature.

While but a single embodiment of the present invention has been here specifically disclosed, it will be apparent that many variations may be made therein, all within the scope of the instant invention as defined in the following claims.

We claim:

1. A thermoelectric generating assembly comprising a chamber unit in which fuel combustion is adapted to take place, said chamber un'it having a heat-transmitting wall a thermoelectric generating module with hot and cold sides, and a heat-dissipating unit having a heat-receiving wall, said module being sandwiched between said heat-transmitting side of said chamber unit and said heat-receiving wall of said heatdissipating unit with its hot and cold sides respectively in operative engagement therewith, and resilient means urging said chamber unit and said heat-dissipating unit toward one another, thereby to retain said module in position, said module comprising a pair of walls having relatively thin, flexible peripheral portions sealed at their edges, a space being defined between said walls, a thermoelectric generating element in said space, said element physically operatively engaging said walls, the interior of said space being at subambient pressure, electrical connections to said element sealingly passing through said walls, said walls further comprising on the outside thereof respectively a pair of relatively thick members of good heat-conductivity in registration with and on opposite sides of said thermoelectric generating element.

2. A thermoelectric generating assembly comprising a chamber unit in which fuel combustion is adapted to take place, said chamber unit having a heat-transmitting wall, a thermoelectric generating module with hot and cold sides, and a heat-dissipating unit having a heat-receiving wall, said module being sandwiched between said heat-transmitting side of said chamber unit and said heat-receiving wall of said heatdissipating unit with its hot and cold sides respectively in operative engagement therewith, and resilient means urging said chamber unit and said heat-dissipating unit toward one another, thereby to retain said module in position, said module comprising a pair of walls having relatively thin, flexible peripheral portions sealed at their edges, a space being defined between said walls, a thermoelectric generating element in said space, said element physically operatively engaging said walls but being free of fastening to said walls, the interior of said space being at subambient pressure, electrical connections to said element sealingly passing through said walls, said walls further comprising on the outside thereof respectively a pair of relatively thick members of good heatconductivity in registration with and on opposite sides of said thermoelectric generating element.

3. A thermoelectric generating assembly comprising a combustion chamber unit, fuel inlet means in fluid communication with said chamber unit, thermoelectric generating means in heat-transfer relation with said chamber unit, gas flow means in fluid communication with said chamber unit and comprising an air inlet means in fluid communication with said chamber unit and first exhaust means for the products of combustion from said chamber unit to the atmosphere, and airflow means operatively communicating connected between said air inlet means and a second and separate exhaust means to the atmosphere externally of said chamber unit and permitting free flow of air through said airflow means and said second exhaust means, thereby to equalize the air pressures at said air inlet means and second exhaust means respectively said airflow means and said gas flow means being so constructed and arranged as to provide separate and distinct airflow paths from said air inlet means to said first and second exhaust means respectively.

4. The assembly of claim 3, in which said airflow means comprises a chamber in free fluid communication with said air inlet means provided with apertures in the sides and end thereof.

5. The assembly of claim 3, in which said airflow means comprises a chamber in free fluid communication with said air inlet means provided with apertures in the sides and end thereof, and a tube extending between and in fluid communication with said chamber and that portion of said assembly where said second exhaust means terminates.

6. The assembly of claim 3, in which said airflow means comprises a chamber in free fluid communication with said air inlet means provided with apertures in the sides and end thereof, and a tube extending between and in fluid communication with said chamber and that portion of said assembly where said second exhaust means terminates, the inner diameter of said tube being appreciably greater than the inner diameter of said first exhaust means. 

2. A thermoelectric generating assembly comprising a chamber unit in which fuel combustion is adapted to take place, said chamber unit having a heat-transmitting wall, a thermoelectric generating module with hot and cold sides, and a heat-dissipating unit having a heat-receiving wall, said module being sandwiched between said heat-transmitting side of said chamber unit and said heat-receiving wall of said heat-dissipating unit with its hot and cold sides respectiVely in operative engagement therewith, and resilient means urging said chamber unit and said heat-dissipating unit toward one another, thereby to retain said module in position, said module comprising a pair of walls having relatively thin, flexible peripheral portions sealed at their edges, a space being defined between said walls, a thermoelectric generating element in said space, said element physically operatively engaging said walls but being free of fastening to said walls, the interior of said space being at subambient pressure, electrical connections to said element sealingly passing through said walls, said walls further comprising on the outside thereof respectively a pair of relatively thick members of good heat-conductivity in registration with and on opposite sides of said thermoelectric generating element.
 3. A thermoelectric generating assembly comprising a combustion chamber unit, fuel inlet means in fluid communication with said chamber unit, thermoelectric generating means in heat-transfer relation with said chamber unit, gas flow means in fluid communication with said chamber unit and comprising an air inlet means in fluid communication with said chamber unit and first exhaust means for the products of combustion from said chamber unit to the atmosphere, and airflow means operatively communicatingly connected between said air inlet means and a second and separate exhaust means to the atmosphere externally of said chamber unit and permitting free flow of air through said airflow means and said second exhaust means, thereby to equalize the air pressures at said air inlet means and second exhaust means respectively said airflow means and said gas flow means being so constructed and arranged as to provide separate and distinct airflow paths from said air inlet means to said first and second exhaust means respectively.
 4. The assembly of claim 3, in which said airflow means comprises a chamber in free fluid communication with said air inlet means provided with apertures in the sides and end thereof.
 5. The assembly of claim 3, in which said airflow means comprises a chamber in free fluid communication with said air inlet means provided with apertures in the sides and end thereof, and a tube extending between and in fluid communication with said chamber and that portion of said assembly where said second exhaust means terminates.
 6. The assembly of claim 3, in which said airflow means comprises a chamber in free fluid communication with said air inlet means provided with apertures in the sides and end thereof, and a tube extending between and in fluid communication with said chamber and that portion of said assembly where said second exhaust means terminates, the inner diameter of said tube being appreciably greater than the inner diameter of said first exhaust means. 